Rotational blade aircrafts, such as single and tandem rotor helicopters, rely upon the lift created by the rotation of their rotor blades to remain airborne. Should the aircraft experience a loss of power or other mechanical failure, other systems must be available to safely land the aircraft.
Most rotational blade aircrafts today are capable of autorotation even during a power outage. Autorotation is the ability of the rotors of a rotational blade aircraft to continue to rotate even without power and to provide sufficient lift to land the aircraft at a safe speed. However, autorotation may not be available in all emergency situations, for example, when the main rotor blade has been damaged.
It has therefore been found advantageous to incorporate emergency parachute systems into rotational blade aircrafts, which deploy a parachute when an emergency situation exists or in other situations where use of a parachute is appropriate. Such parachutes are designed to increase drag when deployed, thus reducing vertical air speed and increasing the chances for a safe landing. Such parachute systems may be used alone or together with autorotation to improve control of the aircraft's vertical air speed.
For example, U.S. Pat. No. 5,836,544 to Gentile discloses a parachute system with forward and aft parachutes connected to structures found on the bottom side of a rotor-type aircraft. The disclosed system adds substantial weight and drag to the aircraft during normal flight operations, and suffers from a high likelihood that parachute lines will be entangled with the main rotor, and of increased moment (torque or bending) loads at the forward and aft portions of the aircraft, which could bend or otherwise damage the aircraft or foul the parachutes.
U.S. Pat. Nos. 2,812,147 to Trabucco and 3,138,348 to Stahmer both disclose parachute support systems wherein a parachute is stored inside a domed housing fixed above the helicopter rotor during normal flight operations. The dome housings are affixed to the top of the helicopters' rotor shafts, thus all loads from the parachute are focused on the tip of the rotor shafts, which may cause mechanical failure due to high moment loads at that point. These systems also require a large number of parts, leading to high weight and complexity, and have high profiles that may cause high drag during normal flight operations.
U.S. Pat. No. 4,709,881 to Rafikian et al. discloses a parachute system for disabled helicopters comprising a parachute housing disposed above and attached to the helicopter's main rotor shaft. Within the parachute housing can be found a platform having rungs for attachment to a parachute. The platform is rotationally separated from the rest of the aircraft through the use of ball bearings. However, the loads from the parachute will be concentrated only at the top of the rotor. This system will therefore be subjected to high moment loads at the tip of main rotor shaft, and the high profile may cause unwanted drag during normal flight operations.
U.S. Pat. No. 6,199,799 to Lai discloses a parachute system for a helicopter wherein a parachute is connected directly to the bottom of a main rotor shaft, which introduces high concentrated loads on the mast. Due to this concentration of load, this system can only be used on small or light helicopters.
Thus, current parachute systems suffer from one or more of the following problems: insufficient or improper rotational separation of the parachute from the rest of the aircraft, high parachute system weight, part count, profile, and complexity, or improper parachute system load pathing, leading to dangerous mechanical stresses. Once a parachute is deployed, most if not all of the entire weight of the aircraft is borne by the parachute. If the load is not transferred between the helicopter body and the parachute in a proper way, mechanical failure or malfunction may occur. A parachute system which is attached only to a single point and offset of the centerline of the aircraft may suffer from high moment loads and moment loads that cause parachute rotation. Parachute rotation may also be caused when there is insufficient rotational separation between the parachute and the aircraft, which could lead to tangling of the parachute's support cables or other mechanical malfunction of the parachute system.
Thus, there is a need for a parachute system for a rotational blade aircraft which distributes the load of the aircraft properly, is rotationally separated from the aircraft, does not create high moment loads on the main rotor shaft or other aircraft parts, has low complexity, low weight, low profile, and does not risk interference between the parachute and other parts of the aircraft.